1. Field of the Invention
The present invention is directed to optical devices, and more particularly to poling of ferroelectric crystal materials to create optical devices.
2. Description of the Related Art
The process of reversing domains in specific patterns in a ferroelectric crystal is used to create many useful optical devices. Domain reversal, or poling, is typically accomplished by placing electrodes on the top and bottom surface of the ferroelectric crystal, then applying a voltage profile to the electrodes. One surface typically supports a single large continuous electrode, while the other surface may support a correspondingly continuous electrode or a ground plane. The applied voltage creates an electric field inside the ferroelectric crystal, and the domains become aligned with the electric field in the regions corresponding more or less to the shape of the electrode. After the applied voltage is discontinued, the domains retain their alignment permanently or until the crystal is re-poled. The electrodes are typically removed upon termination of the poling process.
Unfortunately, the pattern resulting in the poled area does not always correspond sufficiently well or predictably to the electrode shape. Small scale pattern fidelity can be compromised, for example, due to variations in the ferroelectric crystal or crystal-to-electrode contact when domain reversed regions are created over large areas of the surface of the ferroelectric crystal. Pattern fidelity can also be compromised when the electrode pattern contains features of different size and/or shape, inasmuch as the electrical poling voltage profile and current applied to the electrode may not be optimal for all of the features.
Therefore, a need exists for improving the fidelity of domain reversed patterns in ferroelectric crystals.